1. Field of the Invention
The present invention relates generally to the telecommunications field and, in particular, to the transporting of short text messages to subscribers in a wireless telecommunications system.
2. History of Related Art
The Global System for Mobile Communications (GSM) is a digital, mobile cellular radiotelephone system that has been introduced as a standard in several European countries. The basic telecommunications services supported by the GSM include two-way voice communications between fixed and mobile subscribers, CCITT Group 3 facsimile transmissions, and synchronous and asynchronous data transmissions at rates of up to 9.6 kbits/s.
A special telecommunications service supported by the GSM is the Short Message Service (SMS). The SMS enables the GSM to route short text messages, each up to 160 alphanumeric characters long, over the signaling channels to or from mobile stations. If a mobile station for which a short message is intended is not in service, or has left the coverage area, the message is stored in a Short Message Service Center (SMS-C). The SMS-C forwards the message to the mobile station when it returns to service or re-enters the coverage area. The SMS can also transfer short messages between a Short Message Service Terminal (SMT) in a data network and GSM mobile stations.
The GSM is divided into a switching subsystem and base station subsystem. A call from a mobile station is received by a base transceiver station, which is part of the base station subsystem. The base transceiver station defines an individual cell in a geographical service area. A base station controller also in the base station subsystem controls a group of base transceiver stations (cells). A number of base station controllers are served by a mobile services switching center (MSC), which forms a part of the switching subsystem. The MSC controls calls to and from other telephone and data communications systems, such as the Public Switched Telephone Network (PSTN), Integrated Services Digital Network (ISDN), Public Land Mobile Network (PLMN), and various public and private data networks.
If a user in another network (e.g., PSTN) calls a GSM subscriber, the call is connected to a gateway MSC (GMSC). The GMSC finds the location of the GSM subscriber by interrogating a home location register (HLR), which is a database in the switching subsystem. The HLR provides the address of the GSM subscriber in its most current MSC area. The GMSC routes the call to that MSC. The current location of the GSM subscriber is maintained in a visitor location register (VLR), a database containing information about all of the GSM subscribers currently located in that MSC's area. If the GSM subscriber roams into a new MSC area, the VLR associated with the new MSC requests information about the subscriber from the HLR. At the same time, the HLR is informed about the new MSC area in which the subscriber resides.
In the GSM, a short message can be mobile originated or mobile terminated. A mobile originated short message is submitted from a mobile terminal via a base transceiver station to the visited MSC. The visited MSC forwards the message to the SMS-C given by the originating mobile terminal. The SMS-C forwards the message to its destination, which can be a mobile station or a terminal in the data network.
A mobile terminated short message is submitted by a user directly to an SMS-C. The SMS-C forwards the message to a short message service-gateway mobile services switching center (SMS-GMSC). The SMS-GMSC interrogates the related HLR for transporting information, and reroutes the message to the appropriate MSC. The destination mobile station is paged and a connection is set up between the MSC and the mobile station. Upon set up, the MSC forwards the message to the mobile station via the signaling channel (e.g., stand alone dedicated control channel or SDCCH). If the message was delivered successfully, a notification report is sent from the MSC to the originating SMS-C. If not, the HLR is so informed and a failure report is sent from the MSC to the originating SMS-C. The notification report or failure report can be sent to the message originator by the SMS-C.
In order for a user to receive and send text in a short message, certain short message control data is provided to the SMS-C. This control data allows the message originator to specify the destination subscriber to the SMS-C, along with, for example, when (e.g., at 4:00 p.m.) and how (e.g., by facsimile) the text is to be sent to the destination. In the GSM, the SMS has been implemented by the inclusion of an exclusive SMS protocol in parallel with a Q.931 message-oriented call control protocol.
The Q.931 call control interface (also referred to as CCITT Recommendation I.451) is a protocol that specifies what goes into a signaling packet and also defines the message type and content. Specifically, the Q.931 call control interface provides for call setup and take down, the called party number, calling party number information, bearer capability (e.g., voice or data), status checks (for recovery from abnormal events, such as protocol failures or "busy" trunks), release of bearer channels, and error announcements. The Q.931 call control interface is derived from the CCITT Digital Subscriber Signaling System No. 1 (DSS1) user-network ISDN interface.
In other digital mobile radiotelephone systems, such as, for example, the Personal Digital Cellular (PDC) System (also known as the Japanese Digital Cellular Radio System or JDC), and in fixed ISDNs, the Q.931 call control interface has been specified for use, but no parallel SMS interface has been provided. Consequently, although short message text information can be transported in these networks via the existing Q.931 interface, a problem arises in attempting to transport short message control data without a special SMS interface.
A conventional solution to this problem is to include the short message call control data in the Q.931 User-User Information Element (UUIE) field along with the short message text. However, this solution creates another problem, because the more control data that is included in the UUIE, the less text that can be input to the UUIE by the message originator, and the UUIE already has a very limited length (128 octets).
Another problem arises in attempting to send a short message between an MSC and an SMS-C. The conventional technique is to send the short message using the network interface signaling PDC Mobile Application Part (MAP) protocol. In systems other than the GSM, the use of the MAP protocol to transport a short message to a receiving SMS-C is relatively inefficient and thus problematic. For example, fixed ISDNs (and PDC operators) use a number 7 signaling-based ISDN user part (ISUP) protocol. Consequently, the use of a MAP protocol would force the fixed ISDNs (and PDC operators) to introduce and use a MAP protocol over the existing ISUP protocol, which would increase the design complexity significantly and add at least substantial software costs. Furthermore, since many SMS-Cs are integrated with a voice mail system center, and such voice mail system centers use an ISUP protocol to communicate with an MSC, it is advantageous to use that already existing ISUP protocol for communications between the SMS-C and the MSC. Furthermore, using a MAP protocol to transfer a release command between an MSC and SMS-C does not allow the SMS-C to immediately terminate the connection to the MSC, which ties up that circuit for an unnecessarily long period of time.